Fuel cell systems include a fuel cell stack that produces electrical energy based on a reaction between a hydrogen-based feed gas (e.g., pure hydrogen or a hydrogen reformate) and an oxidant feed gas (e.g., pure oxygen or oxygen-containing air). The hydrogen-based feed gas and oxidant feed gas are supplied to the fuel cell stack at appropriate operating conditions (i.e., temperature and pressure) for reacting therein. The proper conditioning of the feed gases is achieved by other components of the fuel cell stack to provide the proper operating conditions.
The fuel cell system includes a compressor for compressing and pumping the oxidant feed gas to an appropriate operating pressure for reaction in the fuel cell stack. The compressor is required to respond to load change requests. For example, when a higher power output from the fuel cell is required (e.g., during a vehicle acceleration event), the compressor must increase capacity to provide the oxidant to the fuel cell at a quicker rate.
The upward transient response time is required to be a change from 10% to 90% capacity in approximately 1 second. Such rapid response times can cause short-term power drain several times the power rating of the compressor motor. Further, power is wasted when current is used to brake the motor during a downward transient (e.g., 90% to 10% capacity).